Well-shaped Mn3O4 tetragonal bipyramids with good performance for lithium ion batteries

Abstract

Well-shaped Mn₃O₄ tetragonal bipyramids with a high reversible capacity of 822.3 mA h g⁻¹ are synthesized by a simple hydrothermal method without any surfactants or coordination compounds. The structural features and morphology of the final product are investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). The SEM and HRTEM results reveal that all the eight exposed facets of the Mn₃O₄ tetragonal bipyramids are indexed to the high-energy {101} planes. The tetragonal bipyramids with high-energy facets provide the Mn₃O₄ anode material with a high initial discharge capacity (1141.1 mA h g⁻¹). In addition, the anode displays a good fast rate performance, delivering a reversible capacity of 822.3 mA h g⁻¹ (the theoretical capacity: 937 mA h g⁻¹) at a current density of 0.2 C after 50 cycles. Moreover, the coulomb efficiency for the first cycle reaches about 66% and remains at about 100% during the subsequent cycles. A relatively detailed growth mechanism of these tetragonal bipyramids is proposed in this manuscript.